The Caliciviridae are a family of positive-sense, single-stranded RNA viruses with a 7–8 kb genome that are divided into 4 distinct genera and further subdivided into genogroups. The genera Norwalk-like viruses, together with the closely related Sapporo-like viruses, recently renamed Noroviruses and Sapoviruses (Mayo, M. A., Arch. Virol. 147:1655–1656, 2002), make up human caliciviruses (Kapikian, A. Z. et al., J. Virol. 10:1075–1081, 1972; Jiangz, X. et al., Science 250:1580–1583, 1990; Jiang, X. et al., Virol. 195:51–61, 1993; Hardy, M. E. et al., Virus Genes 12:287–290, 1996). Noroviruses are responsible for more than 90% of all cases of non-bacterial epidemic gastroenteritis(Kapikian et al., 1972; Kapikian, A. Z. et al., Chapter 25 in Fields Virology, Fields, B. N. et al., Eds., 1996; Pang, X. L. et al., Pediatr. Infect. Dis. J 18:420–426, 1999; Pang, X. L. et al., J. Infect. Dis. 181(Supp. 2):S288–S294, 2000; Fankhauser, R. L. et al., J. Infect. Dis. 178:1571–1578, 1998; Glass, R. I. et al., J. Infect. Dis. 181(Supp. 2):S254–S261, 2000; Hedlund, K. O. et al., J. Infect. Dis. 181(Supp. 2):S275–S280, 2000; Koopmans, M. et al., J. Infect. Dis. 181(Supp. 2):S262–S269, 2000; Inouye, S. et al., J. Infect. Dis. 181(Supp. 2):S270–S274, 2000). There are no current therapeutic drugs or vaccines for these important human pathogens. Sapoviruses are typically associated with sporadic cases of pediatric gastroenteritis (Pang et al., 1999; Pang et al., 2000). Two other calicivirus genera, Vesiviruses and Lagoviruses, contain animal viruses exclusively. Calicivirus genomes typically contain a large 5′ open reading frame (ORF1) encoding a nonstructural polyprotein, followed by ORF2 encoding a single capsid protein. ORF2 is either in frame with ORF1 or present as an independent ORF. While the 5′ end of ORF1 shows extensive sequence diversity, the remainder of ORF1 contains motifs arranged in a specific order conserved between caliciviruses and picornaviruses. ORF3, encoding a basic protein, is present at the 3′ end of the genome preceding a poly-A tract (Clarke, I. N. et al., J. Infect. Dis. 181(Supp. 2):S309–S316, 2000).